Method of forming semiconducting materials and barriers

ABSTRACT

In a gaseous glow-discharge process for coating a substrate with semiconductor material, a variable electric field in the region of the substrate and the pressure of the gaseous material are controlled to produce a uniform coating having useful semiconducting properties. Electrodes having concave and cylindrical configurations are used to produce a spacially varying electric field. Twin electrodes are used to enable the use of an AC power supply and collect a substantial part of the coating on the substrate. Solid semiconductor material is evaporated and sputtered into the glow discharge to control the discharge and improve the coating. Schottky barrier and solar cell structures are fabricated from the semiconductor coating. Activated nitrogen species is used to increase the barrier height of Schottky barriers.

This application is a continuation of application Ser. No. 07/949,753,filed Sep. 23, 1992 now U.S. Pat. No. 5,470,784, which is a continuationof application Ser. No. 07/639,197 filed Mar. 11, 1991 now U.S. Pat. No.5,187,115, which is a division of application Ser. No. 07/394,281 filedAug. 16, 1989 now U.S. Pat. No. 5,049,523, which is a continuation ofapplication Ser. No. 07/180,720 filed Apr. 4, 1988 abandoned, which is acontinuation of application Ser. No. 06/935,606 filed Dec. 1, 1986,abandoned, which is a continuation of application Ser. No. 06/716,409filed Mar. 27, 1985, abandoned, which is a division of application Ser.No. 06/355,202 filed Mar. 5, 1982 abandoned, which is a division ofapplication Ser. No. 06/088/100 filed Oct. 24, 1979 now U.S. Pat. No.4,328,258 which is a division of application Ser. No. 05/857,690 filedDec. 5, 1977 now U.S. Pat. No. 4,226,897.

BACKGROUND OF THE INVENTION

Hydrogenated amorphous silicon films, hereinafter called a-Si, which aresuitable for semiconductor applications have been prepared by a varietyof techniques. Chittick, Alexander, and Sterling reported in the Journalof the Electrochemical Society, Vol 116, No. 1 (January 1969) pages77-81, in an article entitled “The Preparation and Properties ofAmorphous Silicon”, that an inductively coupled, RF glow-discharge insilane (SiH₄) gas produced low-conductivity a-Si films that could bedoped with both donor and acceptor impurities, thereby changing the a-Siconductivity over a wide range of values. More recently, a-Si films wereproduced by evaporating silicon in an atmosphere of hydrogen (H₂) and bysputtering silicon in an atmosphere of H₂+Ar which exhibited similarsemiconductor characteristics to those films made from silane in aglow-discharge.

Presently, several commercial projects related to the development ofSchottky barrier solar cells using crystal, polycrystal, and amorphoussemiconductor materials were described in a recent book entitled TwelfthIEEE Photovoltaic Specialists Conference-1976, published by theInstitute of Electronic and Electrical Engineers Inc., New York, N.Y.,10017. On pages 893-895 of this book, Carlson et al reported in anarticle entitled “Solar Cells Using Schottky Barriers on AmorphousSilicon” that he formed a solar cell by applying a transparent electrodewith appropriate work-function to one side of an a-Si film and an ohmiccontact to the other. Also, this article stated output voltagesincreased initially by 100 mV when the thin metal electrode wasevaporated in residual oxygen background in the vacuum system, producinga metal-insulator-semiconductor (MIS) structure. More recently, Carlsonreported in Vol 77-2 Extended Abstracts, Fall Meeting, Atlanta, Ga.,Oct. 9-14 1977 of the Electrochemical Society, Princeton, N.J., 08540,pages 791-792, that these MIS cells were generally unstable.Furthermore, Carlson reported that his electrodes were less than 0.02cm² in area—a value too small for commercial use. Also, an article byGodfrey & Green in Applied Physics Letters Vol 31, No. 10, (Nov. 15,1977) pages 705-707, indicates that such small areas lead to erroneousdata.

My prior glow-discharge coating processes are covered in U.S. Pat. Nos.3,068,283, 3,068,510 (Dec. 18, 1962) and 3,600,122 (Aug. 17, 1971).These processes generally related to polymeric coatings which haveresistivities greater than 10¹² ohm-cm High-resistivity coatings act asblocking capacitance in series with the glow-discharge thereby assistingin regulation of coating uniformity. However, neither 60 Hz linetransformers nor DC power supplies can be used with my prior processes.The present process, on the other hand, produce semiconducting filmswhich act primarily as resistances in series with the glow discharge andwhich require different process concepts.

SUMMARY OF THE INVENTION

The present coating process is related to producing semiconductor filmswhich have electrical resistivities generally less than about 10¹²ohm-cm at room-temperature, and preferably between 10¹² and 10⁶ ohm-cm.The present process is designed to produce uniform semiconductingcoating over a large area by means of a glow-discharge in which pressureand electric field are controlled. Also, the present process relates tothe treatment of a semiconductor surface to increase the Schottkybarrier voltage when an active conducting coating is applied. Suchtreatment may be used on any semiconductor material, including crystalsemiconductors which have conductivities of 100 and 0.01 ohm cm. andhigher. My coating process and barrier treatment is particularly usefulfor producing a Schottky barrier solar cell.

The principle object of the process is to produce a semiconductor andbarrier for use in a solar cell. Another object of the invention is tocoat a large-area substrate with amorphous semiconducting material. Yetanother object is to form a Schottky barrier between a semiconductingmaterial and an active electrode. Another object is to dope large areaamorphous semiconductor materials to form an ohmic contact with aconducting substrate. Another object is to introduce semiconductormaterial from a solid-source into a coating being formed byglow-discharge deposition from the gas-phase.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view of apparatus illustratingglow-discharge in the weak electric field.

FIGS. 2a-c is a cross-sectional view of devices using semiconductormaterial produced in a glow-discharge and treated with activatednitrogen.

FIG. 3 illustrates another embodiment of the invention in which multipleelectrodes are employed to maintain a glow-discharge.

FIG. 4 illustrates another embodiment in which the substrate is movedthrough the glow-discharge.

FIGS. 5a, b illustrates another embodiment in which the electric fieldconfiguration and pressure are adjusted to enable alternating voltagesto be applied while collecting a substantial part of the semiconductingmaterial.

FIG. 6 illustrates another embodiment in which semiconductor material isevaporated through the glow-discharge to stabilize the discharge andattain desired semiconducting properties.

FIG. 7 illustrates another embodiment in which semiconductor material issputtered through the glow-discharge to stabilize the discharge andattain desired semiconductor properties.

FIG. 8 illustrates another embodiment having a solar thermal-collector.

FIG. 9 illustrates another embodiment having a p-n junction.

DESCRIPTION OF THE APPARATUS AND TECHNIQUES

Referring to FIG. 1 and FIG. 2a, cross-sectional views are illustratedof the glow-discharge apparatus and a typical device made therein. Thesubstrate 1 is a 0.010″ thick stainless-steel plate 11 with rectangulardimensions of 3″×4″ supported by electrode 2. Resistance heater 3 isembedded in ceramic block 3 a which supports and heats electrodes 2, 11.Substrate 1 is positioned in the open face of concave counter electrode4 which has a rectangular cross-section of 4″×5″ defined by side-walls 8and top 9. Top 9 is positioned at least 4½″ above the front surface ofsubstrate 11. Electrode assemblies 1 and 4 are positioned inside anenclosure 6 and header 12 and are joined by appropriate gasket to form agastight seal. Vacuum pump 20 is connected through valve and nipple 13to header 12 to evacuate enclosure 6. Gases G from tanks 17 a-e areconducted through regulated needle valves 16 a-e, manifold line 15, andconnector 14 through header 12 into enclosure 6. Here, gases G areconducted through dielectric tubing 5 and diffusor 7 inside electrode 4.A gap 118 of say ½″ between walls 8 and electrode 2 permits egress ofgases G after passing through glow-discharge P. Gauge VG meters theevacuation of enclosure 6 and pressure of gases G. Gauge VG ispreferably of the capacitance-manometer type which is commerciallyavailable for use with corrosive, condensable gases in the range of0.001 to 10 Torr. Readings from guage VG may automatically regulatevalves 16 through a servo-mechanism to maintain a desired pressure. Apotential V is applied between electrodes 2, 4 from power supply 24 byleads 21, 22 connected through insulated electrical bushings 18, 19sealed in header 12. Protective network 23 prevents damaging sparks.Voltage V and current I are metered as indicated. Resistance heater 3enclosed in ceramic 3 a is connected through leads 45 and electricalbushings 45′ to an appropriate power source (not shown).

In operation, the enclosure 6 is evacuated by pump 20 to a pressurebelow about 0.02 Torr and back-filled with silane (SiH₄) from tank 17 aby opening valve 16 a. Valve 16 a is adjusted to maintain the desiredpressure in enclosure 6 which, for example, may be ½ Torr. Next amixture of 10% phosphine (PH₃) in helium (He) from tank 17 b is admittedinto manifold 15 where it mixes with silane and flows through lines 5, 7to raise the system pressure PG to about 1 Torr. The potentialdifference V between electrodes 2, 4 is adjusted to about 530 voltsinitiating a glow-discharge and the current, I adjusted to about 5 mA.to produce a heavily dopes n⁺ coating 101 on plate 100. Aftermaintaining the discharge for about 1 minute, valve 16 b is closed toshut off the flow of PH₃ and He leaving silane alone. The uniformity andimpurity level of ohmic-layer 101 is not as critical as that of thehigh-resistivity a-Si layer 10. Therefore, ohmic-layer 101 may bedeposited by conventional doped chemical-vapor-deposition (CVD) or othertechniques prior to insertion in the apparatus of FIG. 1.

Next, the pressure PG of silane is adjusted to 0.3 to 0.4 Torr toposition a diffuse discharge P in the region above plate 100 andminimize the discharge in the region of closest separation d betweenelectrodes 2, 4. The discharge then occurs in the weaker region of theelectric-field E as will be discussed in more detail in connection withFIG. 5b. The discharge is maintained for 40 minutes at 5 mA with V inthe range of 500-700 depending on PG. After desired thickness onsubstrate 1 is attained, valve 16 b is closed and the residual gasesevacuated to background by pump 20. Valve 16 c on ammonia (NH₃) tank 17c is opened to admit NH₃ into the substrate region 1 to a pressure ofabout 400 Torr. A potential difference V is applied between electrodes2, 4 of about 350 volts and I of 5 mA produce to a glow-dischargeadjacent coated substrate 1. Valve 16 c is closed, the residual gases inenclosure 6 evacuated by pump 20, and the enclosure 6 is backfilled withnitrogen from tank 17 d (valve 16 d) to purge unreacted silane. Valve 13is closed, jar 6 raised to atmospheric pressure and substrate 1 removed.

Referring to FIG. 2a, the substrate 1 is illustrated with foil 100coated with n⁺-doped a-Si layer 101, undoped 1-4 μm a-Si layer 10 andammonia-treated layer 30. The substrate 1 is then placed in aconventional vacuum-evaporator and coated with a high work-function,semi-transparent metal 31 (such as palladium) to a thickness of about100 A or less to complete the Schottky barrier. The conducting layer 31is adjusted to be thick enough to reduce its sheet resistance while notabsorbing an inordinate amount of incident photons. A grid 32 of thickermetal such as a silver-titanium alloy (Ag-Ti) is applied to reduce theseries resistance of the semi-transparent electrode 31. Also, a topanti-reflection (AR) layer 33 such as Si₃N₄ with a thickness range ofabout 1000 A^(∘) may be applied to electrode 31 to reduce reflectionloss under photon irradiation. Under test using AM1 illumination and aTektronics Corp. curve tracer, the short-circuit current Isc wasmeasured to be about 2 mA/cm² and the open-circuit voltage Voc was about350 mV, with no AR coating and 50% reflection loss. When the layer 30was added by the NH₃ discharge, Isc remained about 2 mA/cm² while theVoc was measured to be greater than 600 mv—an increase in excess of 250mV, again with no AR coating. Similar increases were found with othersubstrates as illustrated in the following drawings.

Referring to FIG. 2b, a glass substrate 104 coated with a transparentconducting coating 105 of the oxides of indium (In) and tin (Sn)(commercially available) may be inserted into the apparatus of FIG. 1 onelectrode 2 with the conducting coating 105 facing the discharge andconducting tab 106 contacting electrode 2. Thereafter, the coatingprocedure is the same as that described in connection with FIG. 2a, inthat ohmic contact layer 39, a-Si layer 80, NH₃-treated barrier-layer 41are produced sequentially. Also, using an evaporator, a Pd coating 82 isapplied to complete the Schottky barrier and a thicker metallic layer 43such as Ti-Ag applied to complete the contact. When substrate 1 isilluminated in operation through the glass substrate 104, electrode 43may be opaque. An additional AR coating 107, such as an oxide oftantalum, may be applied to the glass. Although the glass substrate 104serves as a useful protective material, the configuration of FIG. 2bproduces somewhat less output than that of FIG. 2a since the maximumnumber of charge carriers are generated at the ohmic surface where theincident photons impinge first rather than at the barrier where theoutput potential is developed.

Referring again to FIGS. 2a, b, p-type a-Si may be substituted for then-type a-Si in coatings 10, 41 by doping with a donor impurity duringformation in the apparatus in FIG. 1. For example, during formation ofthe a-Si coating 10, the apparatus of FIG. 1 may be operated asdescribed above except that diborane from tank 17 e (valve 16 e) isadded to the silane flow from tank 17 b to dope the a-Si layer 10 toneutral or to p-type depending on the fractional amount of B/Si.Correspondingly, 1-10% diborane from tank 17 e may be added to G to dopethe ohmic-layer 101 to p⁺ level. For p-type a-Si, the active metal layer31 is formed from a low work-function metal such as chromium (Cr) oraluminum (Al). In either case the layers 30, 40 may be formed byNH₃-discharge to enhance the Schottky barrier with any of the structuressuch as shown in FIGS. 2a, b, c.

Referring again to the apparatus of FIG. 1, I found that barrier-heightand Voc of an untreated a-Si material may be increased byglow-discharging in N₂ gas instead of NH₃. However, using the structureof FIG. 2a, when layer 30 was formed from a N₂ discharge the increase inVoc amounts to only about 100 mV instead of 250 mV with NH₃. Also,nitrogen atoms (N·) produced an increased barrier. For example, using acommercial plasma torch producing a nitrogen atom beam to treat thesurface 10, Voc increased by 150 mV after 15 minutes treatment. Thisvalue is somewhat larger than the direct N₂ discharge but smaller thanthe 250 mV under direct NH₃ glow-discharge. Hydrazene proved moreeffective than N₂ alone. Air in an atomic beam was found to increase theVoc also; however, oxygen alone in a glow-discharge formed a blockinglayer. The discharge for producing the NH₃ treated layer 30 is not ascritical as that for producing the a-Si layer 10 since the gases, perse, do not form a film but combine with the coating 10, depositedpreviously. The glow-discharge time-limits are determined by thelimiting thickness through which charge carriers can tunnel.

Referring to FIG. 2c, the substrate 1 is 0.0035″ thick stainless-steelfoil 102 reinforced with frame 109 which may be {fraction (1/16)}″ orthicker, to prevent foil 10 ₂ from bending in a small radius anddamaging the a-Si film 110. Again, a barrier layer 111 is formed bydischarge treatment in ammonia. However, an additional barrier layer 112is added which nay be antimony trioxide (Sb₂O₃) or titanium dioxide(TiO₂) or other metallic oxides or nitrides having a thickness 50 A^(∘)or less to enhance the barrier height without blocking the desiredcharge carriers. In the case of TiO₂, the semi-transparent layer 36 maybe nickel (Ni) with a thickness 100 A^(∘) or less and may have anadditional conducting layer of 50 A^(∘) or so of chromium (not shown).Contact fingers 35 and AR coating 33 are added to complete thephoto-voltaic Schottky barrier. The cells of FIGS. 2a, b, c may be madewith any semiconductor material having a photoresponsive barrier such asthat made in the following apparatus.

Referring to FIG. 3, the anode 4 of FIG. 1 is replaced by a set ofcylindrical pins 80 supported by a dielectric holder 81. Each pin 80 isconnected through protective resistors 82 to +V. The surfaces ofdielectric holder 81 and resistors 42 are positioned at least about 6″above the substrate 1 to avoid deposition of conducting silicon material(M noted in FIG. 1). Typical operating conditions are similar to thosedescribed in connection with FIG. 1 in that the desired gases G areadmitted through a suitable distributor (not shown) and exhausted by apump (not shown) except that the pressure and current density can beoperated at higher values say up to 2 Torr and 1 mA/cm² and higher.Also, substrate 1 can be moved through the discharge for continuouscoating or may remain static. Again, the fringing field lines E permitthe discharge to move up the pins 80 by adjustment of pressure whilemaintaining the discharge in the weaker field E_(w).

Other geometries can be used for pins 80 such as tapered pins or hollowcylinders facing the substrate 1. Silicon which is collected on the pins80 represents wasted material. However, I found that by applying DC orDC plus AC with the pins 80 biased anodically, silicon collection isminimized. For designing protective resistors 40, if the average currentdensities (I/area) to substrate 1 is adjusted to be 0.2 mA/cm² and withpins 80 1 cm apart, resistors may be in the range of 100 k ohms for goodregulation. Hollow pins are described with a moving substrate in FIG. 4.

Referring to FIG. 4, an in-line system is illustrated schematicallyusing hollow electrodes 70 with configuration similar to that in FIG. 3.A loading chamber 60, airlock 61, ohmic-layer deposition system 62, anda-Si deposition-system 63 produce continuously coated substrates 1 suchas those shown in FIGS. 2a, b, c. Finally, chamber 64 treats the coatedsubstrate with activated ammonia species to form the barrier-layer.Appropriate gases G1, G2, G3 are distributed through lines 75, 76, 77into ceramic chambers 78, 79, and 80 which may conveniently houseelectrodes 71, 72, 70 respectively. The gases from distributors 78, 79,80 flow through hollow pins 71, 72, 70 into pumping ports 65, 66 and areexhausted by pumps (not shown). Pressures in ports 65, 66 are adjustedto be below that in compartments 62, 63, 64 to insure that the exhaustgases G do not flow into adjacent compartments. In operation, the sizeof each compartment 62, 63, and 64 is adjusted for the dischargeresidence time to produce the desired coating thickness. Resistanceheaters 67, 68, 69 maintain the substrate 1 at the desired temperatures.The temperature of the substrate 1 in the a-Si region 63 should bebetween 200° and 350° C., whereas the temperature in the ohmic-layerregion 62 can be considerably higher. The temperature in the NH₃ region64 should be below about 300° to advoid dehydrogenation of the a-Si.

In operation, airlock 61 is closed and the substrate 1 which, forexample, are one meter square stainless steel plates, are loaded inchamber 60 and the air is evacuated. Air lock 61 is opened and acommercial feeder mechanism, (not shown) moves the substrate 1 alongguide-rail 48 which acts as the electrical connection to ground forsubstrate 1. Suitable mechanical mechanisms include individual movingarmatures, endless conveyor belts and ultrasonic walkers. Substrate 1 isunloaded and collected in a stacking mechanism (not shown) incompartment 27. Air lock 68 is closed and coated substrates 1 moved tothe evaporation system as described in connection with FIG. 1.Alternatively, loading and unloading compartments 60, 27 could bereplaced with continuous seals, which are standard in the vacuum coatingindustry, to provide vacuum to air operation. Other suitable electrodeconfigurations such as those described in FIG. 5 may be used with amoving substrate.

Referring to FIG. 5a, the preferred embodiment, electrodes areillustrated which enable the use of AC and efficient collection on thesubstrate 1 of a substantial part of the a-Si. Parallel, rectangularelectrodes 92, 93 hold stainless steel plates 90, 91 forming substrateassembly 1. End tabs 92 a, 93 a on electrodes 92, 93 insure goodelectrical contact to substrates 90, 91 and may act as guides ifsubstrates 90, 91 are moved during deposition. Electrical contact toelectrodes 92, 93 is made by leads 96, 97 having ceramic insulators 98,99. Leads 96, 97 are connected to center-tapped transformer 152. Theplates may be supported by leads 96, 97 and additional insulators (notshown). Electrodes 92 are heated, for simplification of theillustration, by resistance-heater 95, ceramic insulation 94, andsupported by a suitable ceramic rod 84. A small gap 88 is maintainedbetween heater insulation 94 and electrodes 92, 93 to advoidshort-circuiting electrodes 92, 93 through conducting Si, which depositsor insulation 94. Also, dielectric members 98, 99, and 84 should extenda distance greater than about 6″ from the region of electrodes 90, 91under glow-discharge. Input gases G are distributed and exhausted fromlines (not shown) as described in connection with FIG. 1.

In operation, silane gas G is admitted to a pressure of about 0.4 Torrand, when electrodes 92, 94 have a minimum separation of ½″, a RMSvoltage of about 650 volts between electrodes 90, 91 from 60 Hztransformer 152 produces a current of 5 mA or about 0.2 mA/cm². Theseoperating values are similar to those 90, 91 used with the DC supply ofFIG. 1, except that each plate becomes cathodic alternately. Asillustrated in FIG. 5b, the negative glow encircles plates 90, 91 in theweak electric field E_(w) and, for ½″ separation d, a silane pressure of0.35 Torr eliminates all glow-discharge in the strong field E_(s). Theactual operating pressure of 0.40 Torr allows some discharge to theinactive ends. The pressure used during deposition of the ohmic-layerand NH₃ treatment is determined separately.

In practice, I found that transformer 152 of the neon-sign type wasconvenient for developmental-size models. In production, larger,self-regulating SCR, or saturable reactor transformers can be used. Linefrequencies (50-60 Hz) and audio frequencies to 20K Hz which aresupplied from inexpensive solid state supplies, are the preferred powersources.

Referring to FIG. 6, an e-beam evaporation source 160 (commerciallyavailable) having an electron gun 50, magnetic deflector 51, andcrucible 52 with electrical contact 53, is used to evaporate polycrystal(pxSi) 164 through a glow-discharge P onto substrate 1. Substrate 1 iscomprised of stainless steel plate 54 retained on electrode 55 andheater 56 in ceramic enclosure 57 as discussed in connection with FIG.1, however, electrodes 54, 55 are attached to arm 58 mounted on shaft59. Shaft 59 may be rotated by a conventional mechanism (not shown) tomove plate 54 from the coating region above source 160 to the vacuummetallization region (not shown) to apply electrodes as described inconnection with FIGS. 2a, b or the TiO₂ barrier layer, as described inconnection with FIG. 2c. Baffle plate 89 and a high-capacity blower-pump(not shown) permit a low pressure in the evaporator region 160 and ahigher pressure in the glow-discharge region P around substrate 1.

In operation, the crucible 56 may be grounded by lead 53 and a potential−V is applied to substrate 1 to maintain the glow-discharge P in gasesG. A negative potential −V may be applied to the e-beam source 50 tobombard and heat crucible 56, or other suitable heat sources may be usedto heat crucible 56 to evaporate silicon 164. Evaporated Si passesthrough the glow-discharge P where it is partially ionized and joins thesilane ions to coat the surface of plate 55. The evaporated materialstabilizes the glow-discharge P and improves the semiconductingproperties of the coating on plate 55. Gases G may be doped, undoped, orNH₃ as discussed in connection with FIG. 1. However, additional dopingmay be applied from the material in crucible 56. Also, any of thestructures illustrated in FIGS. 2a, b, c may be formed and ammonia maybe added without operating evaporation source 160.

Referring to FIG. 7, a sputtering source 89 of the inverted magnetrontype such as I described with E. G. Linder and E. G. Apgar inProceedings of the IRE (now IEEE) (July 1952), pages 818-828. The source89 has a cylindrical electrode 85 composed of poly-crystal Si, endplates 87, anode ring 86, and magnetic field B with its principlecomponent longitudinal to the axis of the electrode 85. The substrate 1has plates 114, electrodes 115, heater dielectric 116 and element 117similar to substrate 1 described in connection with FIG. 1. Substrate 1is positioned to receive silicon sputtered from electrode 85. Apotential −V relative to ring 86 maintains a glow-discharge ininput-gases G in the vicinity of the surface of plate 114.

In operation, gases G10 such as Ar or Ar+H₂ are infected betweenmagnetron electrodes 85, 86. A suitable potential, +V, on anode 86 andmagnetic field B are maintained to sputter silicon onto the surface ofplate 114. At the same time, a potential −V is applied to substrate 1relating to electrode 85 to maintain a glow-discharge P in gases G10 andsputtered silicon from source 85. The potential −V is maintained untilthe ions in glow-discharge P deposit on substrate 114 to form a film ofthe desired thickness. Silicon from the sputter source 89 facilitatesmaintainance of a uniform glow-discharge in the vicinity of substrate 1and improves conductivity characteristics of Schottky barriers such asillustrated in FIGS. 2a, b, c.

Although I have used for convenience silane gases in the illustrations,other silicon-hydrogen gases can be used such as SiHCl₃ and SiH₂Cl₂.Also, other semiconductor gases such as germane can be used to formhydrogenated amorphous germanium. Non-hydrogenated semiconductors canalso be used with the present invention including the binary alloys ofgallium. For example, trimethylgallium gas glow-discharged with severalother gases forms semiconductor films with arsene, forms GaAS; with NH₃,forms GaN; and, with PH₃ forms GaP. Apparatus illustrating other devicesutilizing such semiconductor films are shown in FIG. 5. and the otherdrawings.

Referring to FIG. 8, a solar thermal-collector is shown with a 1 μm a-Sifilm 121 and a-Ge film 122 coated on the front of stainless-steel plate123 assembly which faces the solar radiation. Water 124, is circulatedby input tubing 125 and output tubing 126 through enclosure 127 where itcontacts the rear of plate 123. Transparent glazing 129 such asplate-glass, and enclosure 128 holds and insulates plate assembly 123which is elevated in temperature by the solar radiation.

Under illumination, the visible solar radiation component which passesthrough glazing 12 is absorbed in the a-Si coating 121. The infra-red(IR) component of the solar radiation passes through the a-Si coating121 and is absorbed in the a-Ge coating 122. Plate 123 preferably has apolished or metallized surface with low IR emissivity for radiationwavelengths above say 2 μm—which would otherwise be radiated from thesolar-heated plate 123, itself. Thus, the a-Si absorbs visible radiationwhereas a-Ge, which has a smaller band gap than a-Si, absorbs the IRcomponent. The a-Si, a-Ge films 121, 122 in combination yield close tothe ideal characteristics of a solar thermal-collector-high absortivityand low IR emissivity. Any of the processes described above may be usedto coat the a-Si and a-Ge layers 121, 122. Also, the coated plateassembly 123 may be used separately without glazing 129 and box 128 as aselective surface in a focused collector (not shown). It should be notedthat both a-Si and a-Ge formed in my apparatus absorb more efficientlythan crystal Si or Ge, and cost substantially less than crystals.Another application of films made with the process is shown in FIG. 9.

Referring to FIG. 9, a p-n junction is shown with a stainless steelsubstrate 131 coated with a-Si film 132 which has a heavily doped n⁺layer making ohmic-contact with plate 131 as described in connectionwith FIG. 1. A p (or pp+) layer 134 is added to coating 132 forming ap-n junction. Top Cr contact layer 135 may be semi-transparent, if thedevice of FIG. 9 is operated as a solar cell. Alternate substrate 131surfaces include alloys of antimony (Sb) and gold (Au).

Other applications of the coating process and the improved barrier-layerare field-effect-transistors FET,insulated-gate-field-effect-transistors IGFET, andcharge-coupled-devices CCD.

What is claimed is:
 1. A method of fabricating a semiconductor devicecomprising the steps of: providing first and second evacuableenclosures; providing a substrate in said first evacuable enclosure;heating said substrate; introducing a first gaseous material into saidfirst evacuable enclosure at a first subatmospheric pressure; isolatingsaid first evacuable enclosure from the external atmosphere; maintaininga first glow discharge that ionizes at least a portion of said firstgaseous material to produce first ionized products; attracting at leasta portion of said first ionized products onto at least a portion of asurface of said substrate to produce a first film on said portion ofsaid surface of said substrate; removing said substrate from said firstevacuable enclosure; placing said substrate in said second evacuableenclosure; introducing a second gaseous material into said secondevacuable enclosure at a second subatmospheric pressure, at least one ofsaid first and second gaseous materials comprising a halogen; isolatingsaid second evacuable enclosure from the external atmosphere;maintaining a second glow discharge that ionizes at least a portion ofsaid second gaseous material to produce second ionized products;attracting at least a portion of said second ionized products onto atleast a portion of a surface of said first film to produce a second filmon said substrate; and removing said substrate from said secondevacuable enclosure.
 2. The method of claim 1 wherein one of said firstand second gaseous materials comprises silicon.
 3. The method of claim 1wherein one of said first and second gaseous materials comprisesphosphorous.
 4. The method of claim 1 wherein one of said first andsecond gaseous materials comprises nitrogen.
 5. A method of making asemiconductor device by forming a film on a substrate using a glowdischarge maintained in a first vacuum chamber between first and secondelectrodes positioned in a face-to-face relation, said first vacuumchamber being one of a plurality of vacuum chambers, said methodcomprising the steps of: disposing said substrate on said firstelectrode; introducing a gaseous film-forming material comprisingsilicon and hydrogen from an external source through said secondelectrode at sub-atmospheric pressure toward said substrate such thatsaid gaseous material flows with a radially outward component of flowover said substrate while isolating said gaseous film-forming materialin said first vacuum chamber from gases in any other chamber of saidplurality of vacuum chambers; and, maintaining between said electrodes aglow discharge that partially ionizes said gaseous material to form afilm comprising silicon and hydrogen on said substrate.
 6. The method ofclaim 5, wherein the step of maintaining a glow discharge comprises:applying a voltage between said electrodes; and, adjusting pressure insaid first vacuum chamber to position said glow discharge above saidsubstrate.
 7. The method of claim 5, wherein the step of maintaining aglow discharge comprises: applying a voltage between said electrodes,said voltage comprising low frequency components.
 8. The method of claim7, wherein said low frequency components comprise line frequency.
 9. Themethod of claim 7, wherein said low frequency components comprise audiofrequency.
 10. The method of claim 5, wherein the step of maintaining aglow discharge comprises: applying to said first electrode a negative DCbias.
 11. The method of claim 10, wherein the step of maintaining a glowdischarge further comprises: applying to said first electrode an ACvoltage.
 12. The method of claim 5, wherein said gaseous materialfurther comprises ammonia, said film further comprising nitrogen. 13.The method of claim 5, wherein said film is a uniform film havingelectrical properties such that said semiconducting device comprisesfield-effect transistors.
 14. The method of claim 5, wherein said filmis a uniform film having electrical properties such that saidsemiconducting device comprises insulated-gate field-effect transistors.15. a method of making a semiconductor device by forming a film on asubstrate, said method comprising the steps of: inserting a plurality ofsubstrates into a vacuum chamber; closing an airlock in communicationwith said vacuum chamber to isolate said vacuum chamber from atmosphericconditions; removing one of said plurality of substrates from saidvacuum chamber; rotating said removed substrate about an axis;positioning said removed substrate into a selected one of a plurality ofprocess chambers arranged about said axis; isolating said selectedprocess chamber from other process chambers and from said first vacuumchamber; introducing a gaseous film forming material comprising siliconand hydrogen from an external source into said selected process chamber;and, maintaining a glow discharge in said selected process chamber thatpartially ionizes said film forming material to form a film comprisingsilicon and hydrogen on said removed substrate.
 16. The method of claim15, wherein said gaseous material further comprises ammonia, said filmfurther comprising nitrogen.
 17. The method of claim 15, wherein thestep of positioning said substrate comprises placing said substrate on afirst electrode, and wherein the step of maintaining a glow dischargecomprises: applying a voltage between said first electrode and a secondelectrode, said first and second electrodes having a face-to-facerelation; and, adjusting pressure in said selected process chamber toposition said glow discharge above said substrate.
 18. The method ofclaim 17, wherein said voltage comprises low frequency components. 19.The method of claim 15, after said film is formed on said substrate,further comprising the steps of: removing said substrate from saidselected process chamber; rotating said substrate about said axis; and,placing said substrate into said first vacuum chamber.
 20. The method ofclaim 19, further comprising the steps of: isolating said vacuum chamberfrom said plurality of process chambers; opening said airlock; and,removing said processed substrate.
 21. A method of making semiconductordevices by forming films on substrates, said method comprising: closingan airlock between a loading chamber and a plurality of process chambersarranged about an axis; inserting a plurality of substrates into saidloading chamber; evacuating said loading chamber; opening said airlock;removing a first substrate of said plurality of substrates from saidloading chamber; rotating said substrate about said axis; positioningsaid first substrate into a process chamber selected from said pluralityof process chambers; isolating said selected process chamber containingsaid first substrate so that said selected process chamber issubstantially free from gases introduced into any other process chamber;removing a second substrate from said plurality of substrates from saidloading chamber while said first substrate is in said selected processchamber; rotating said second substrate about said axis while said firstsubstrate is in said selected process chamber; positioning said secondsubstrate into a different process chamber of said plurality of processchambers while said first substrate is in said selected process chamber;isolating said different process chamber containing said secondsubstrate so that said different process chamber is substantially freefrom gases introduced into any other process chamber; introducing agaseous film forming material comprising silicon and hydrogen into saidselected process chamber any time after insuring that said selectedprocess chamber remains substantially free from gases introduced intoany other process chamber of said plurality of process chambers;maintaining a glow discharge in said selected process chamber thatpartially ionizes said film forming material to form a film comprisingsilicon and hydrogen on said first substrate; and processing said secondsubstrate in said different process chamber.
 22. The method of claim 21,wherein rotating said first and second substrates occurs in an evacuatedzone between said loading chamber and said selected and differentprocess chambers, respectively.
 23. The method of claim 21, wherein saidfilm is a uniform film having electrical properties such that saidsemiconducting devices comprise insulated-gate field-effect transistors.24. The method of claim 5, wherein said film is a uniform film havingelectrical properties such that said film and said substrate comprise asemiconducting device comprising a insulated-gate field-effecttransistor.